Bone fusion systen

ABSTRACT

A method and system for performing bone fusion and/or securing one or more bones, such as adjacent vertebra, are disclosed. The screws include a threaded tip connected to a main shaft and a threaded outer sleeve that rotates relative to the outer shaft until locked down. Independent rotation of the threaded outer sleeve relative to the threaded distal tip allows compression or distraction to modify the gap between the vertebral bodies. The screws are passed from the inferior to superior vertebra or superior to inferior, for example, through a transpedicular route to avoid neurological compromise. At the same time, the path of screw insertion is oriented to reach superior or inferior vertebra. An intervertebral cage of the system is configured for lateral expansion from a nearly straight configuration to form a large footprint in the disc space. The screws and cage may be combined for improved fixation with minimal invasiveness.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/718,786, filed Sep. 28, 2017. U.S. patent application Ser. No.15/718,786 is a continuation of U.S. patent application Ser. No.14/347,442, filed Mar. 26, 2014, which is a 35 U.S.C. § 371 nationalphase entry of PCT Application No. PCT/US2012/058968, filed Oct. 5,2012. PCT Application No. PCT/US2012/058968 claims the benefit ofpriority to U.S. Provisional Application No. 61/543,482, filed Oct. 5,2011. Each of these applications are incorporated by reference in theirentireties for all purposes.

FIELD

This invention relates to neurosurgical and orthopedic fixation systemsand more particularly to bone fusions.

BACKGROUND

Spinal interbody fusion is frequently performed procedure to treatvarious disorders such as degenerated disk disease, spondylolisthesis,trauma, infection, tumor and deformity. Usually, surgery involvesplacement of screws into the vertebral body through the vertebralpedicle and/or placement of an interbody cage with bone grafts into thedisc space. Types of spinal fusion depend on the approach type such asposterior, transforaminal, lateral, etc. Although these approaches claimto be minimally invasive, they still require open incisions for cage andscrew placement. For example to perform one level interbody fusion thesurgeon must perform an incision to perform discectomy and insert acage, then four incisions to insert pedicle screws and then two moreincisions to pass rods and stabilize screws to rods.

During spine stabilization operations a certain degree of compression ordistraction is usually applied to stabilized vertebrae depending on thecondition. Compression is usually performed on the concave side of thescoliotic deformity to correct it.

Distraction on the other hand is opposite to compression and isperformed usually to decompress vulnerable structures that travelbetween vertebrae, i.e. nerve roots. Distraction is usually performed soas to increase the gap between vertebral bodies to decompress nerveroots escaping from neural foramina. It is also is performed on theconvex side of scoliotic deformity.

Improvements in fusion, compression and distraction methods and devicesare therefore desired.

SUMMARY

Implementations of the present disclosure overcome the problems of theprior art by providing a bone screw including a threaded tip, a mainshaft and a threaded outer sleeve. The main shaft has a proximal end anda distal end, wherein the distal end of the main shaft is connected tothe threaded tip and extends proximally therefrom. The threaded outersleeve has a proximal end and a distal end and defines an axial opening.The axial opening extends between the proximal and distal ends. Theaxial opening has a diameter that is greater than the proximal end ofthe main shaft so that the threaded outer sleeve can extend over andfreely rotate about the proximal end of the main shaft.

The bone screw may include a stop member coupled to the main shaftproximal to the threaded tip. The stop member is configured to abut thethreaded outer sleeve during rotation thereof to stop translation of thethreaded sleeve relative to the threaded tip.

The proximal end of the main shaft may include a driver interface and aproximal end of the threaded outer sleeve may have a driver interface,allowing each to be driven by drivers with matching interfaces.

A fastener may be included in the bone screw, wherein the fastener isconfigured for attachment to the proximal end of the main shaft so as tolock the threaded outer sleeve between the fastener and the stop. Forexample, the fastener may be a nut and the proximal end of the shaft mayinclude threads configured to mate with the nut.

The threaded outer sleeve may have threads with a different (larger orsmaller) pitch than the threads of the threaded tip so as to haveanti-rotation properties. Also, the threads may have an oppositeorientation, right versus left-handed, for further anti-rotationproperties.

The threaded tip may have an axial opening configured to allow itspassage over a working wire. Also, the main shaft may have an axialopening to allow its passage over a working wire.

The screw may also include a cage having an outer diameter equal to adiameter of the threaded tip. The cage may be a cylinder defining aplurality of holes between a proximal end and a distal end. And, thedistal end of the cage may include a locking surface configured to matewith a proximal surface of the threaded tip. The cage may be configuredto slide over the stop member.

A method of relatively moving at least two of the bones may use the bonescrew. For example, the method may include advancing a linearly arrangedthreaded distal tip and externally threaded proximal outer sleevethrough a proximal one of the bones and into a distal one of the bonesuntil the proximal outer sleeve extends at least partially within theproximal bone and the threaded distal tip extends at least partiallywithin the distal bone.

The method includes rotating the proximal outer sleeve relative to thethreaded distal tip so as to translate the proximal bone relative to thethreaded distal tip and the distal bone.

For example, rotating the proximal outer sleeve in one directiontranslates the proximal bone away from the threaded distal tip and thedistal bone. Rotating the proximal sleeve in the other directiontranslates the proximal bone toward the threaded distal tip and distalbone.

Rotation of the proximal outer sleeve relative to the threaded distaltip may be facilitated by holding the threaded distal tip while rotatingthe proximal outer sleeve. For example, holding the threaded distal tipmay include engaging a proximal end of a main shaft connected to thedistal tip.

Prior to rotating the threaded distal tip, a fastener may be removedfrom the proximal end of the main shaft. Also, a stop member coupled tothe main shaft may be abutted by the proximal outer sleeve duringrotation.

Also, a fastener may be attached, or reattached, to the main shaft afterrotating the proximal outer sleeve. For example, a nut may be attachedvia threads onto threads of the distal end of the main shaft, therebylocking the outer sleeve against the stop or the threaded distal tip.

The method may also include advancing a cage positioned between thethreaded distal tip and outer proximal sleeve, with the threaded distaltip and proximal sleeve until the cage is positioned in the disc space.Prior to advancing the cage, it may be filled with a bone graft orfusion material. The bone or fusion material may communicate with bonesthrough holes defined in the cage.

An intervertebral cage may be used to facilitate fusion between twovertebral endplates. The cage may include a plurality of links and aplurality of hinges. The links, such as four links, may beinterconnected at adjacent portions by the hinges. The links preferablyhave a height configured to hold the vertebral endplates apart at atherapeutic distance.

Two of the links may have a first length and another two of the links asecond, different length. The first length may extend within ananterior-posterior distance of the endplates and the second length maybe configured to extend within a medial-lateral distance of theendplates.

A pin may be included to secure two adjacent links by sliding the pininto an opening defined by the adjacent links, thereby locking them intoa predetermined angular position. One of the pin or the openings mayinclude a locking mechanism configured to secure the pin within theopening. For example, the locking mechanism may include a detent in thepin or a spring loaded mechanism on the pin and/or links.

The predetermined angular position may be 90 degrees which, for fourlinks, forms a square or a rectangle.

The links may define an opening in one side, the opening configured toreceive a bone filling. Covering the opening may be a door and a hingeconnected to the door.

The links may be configured to collapse into a relatively linearconfiguration with pairs of the links positioned adjacent each other.

A method of facilitating fusion of a pair of adjacent vertebralendplates may include inserting a linkage between the adjacent vertebralendplates through a small percutaneous opening. Also, two of theproximal links may be opened at the proximal hinge to form a proximalangle. Opening of the two proximal links simultaneously urges open twodistal links of the linkage at a distal hinge to form a distal angle.

Opening may include forming equal proximal and distal angles. Openingmay also include urging the distal links with ends of the proximal linksthrough middle hinges separating the proximal and distal links. Theproximal and distal angle may both be 90 degrees.

The cage may be locked into position by inserting a pin through the twoproximal links.

One of the proximal links may be extended in a medial-lateral directionand the other one of the proximal links may be extended in theanterior-posterior direction.

A bone filling may be passed through an opening in one of the linkagesto a position between the links of the linkage.

Before insertion, the linkage may be collapsed into a relatively linearconfiguration with pairs of the links positioned adjacent each other soas to fit through a relatively small surgical opening.

Another bone screw includes a proximal sleeve, an inner post, a distalscrew portion and a stabilizer. The proximal sleeve defines an axialbore having a proximal end and a distal end. The proximal end of theaxial bore includes a plurality of inner threads. The inner post has ahead and a shaft. The shaft of the inner post extends through the axialbore of the proximal sleeve and the head is positioned within theproximal end of the axial bore. The distal screw portion is connected tothe shaft of the inner post. The stabilizer has a plurality of threadsand a driving feature. The stabilizer is configured to be advancedwithin the proximal end of the axial bore of the proximal sleeve alongthe threads until abutting the head of the inner post. Furtheradvancement of the stabilizer distracts the distal screw and proximalsleeve.

The proximal sleeve may have a plurality of outer threads extendingaround an outer surface. The distal screw portion may also include aplurality of outer threads extending around an outer surface.

The distal screw portion may have an inner bore wherein the shaft of theinner post is press fit within the inner bore.

The proximal sleeve includes at least one non-cylindrical outer surfaceconfigured to mate with a driver. This surface, for example, may be partof a hexagonal cross-section.

The head of the inner post may define a driving receptacle, such as ahexagonal cross-section. The driving feature of the stabilizer may be anon-cylindrical through-bore, wherein the non-cylindrical through boreand driving receptacle are configured for alignment for simultaneousdriving of the inner post and the stabilizer.

The distal screw portion may include a proximal end and a distal end.The proximal end of the may have an ingrowth surface configured tofacilitate bone ingrowth. The ingrowth surface, for example, may have atextured pattern, such as a knurled pattern. The textured pattern may beconfigured to hold bone growth promoting compounds, such as bone chips.The distal end of the distal screw may have a tapered shape bearing theplurality of outer threads. Also, the distal end of the distal screwportion may have a distal-most point.

The bone screw may include a connector which includes the stabilizer anda trap. The trap includes a pair of arms having inner threads. Theproximal sleeve may include a proximal end and a distal end. Theproximal end of the sleeve defines the proximal end of the axial bore.The distal end of the sleeve defines the distal end of the axial bore.Also, the proximal end of the sleeve may define a pair of U-shapedslots. The arms of the trap may be configured to fit within the U-shapedslots of the proximal end of the proximal sleeve. The threads of thestabilizer are configured to advance along both the inner threads of thepair of arms and the proximal end of the axial bore to distract thedistal screw and proximal sleeve.

The trap may further include a base and a cap. The arms extend away fromthe base and the cap is configured to fit between the free ends of thearms to retain the stabilizer therein.

A method of relatively moving at least two bones includes advancing adistal screw portion into one of the bones. A proximal sleeve isadvanced into another one of the bones. And, the method includesadvancing a stabilizer within an axial bore of the proximal sleeveagainst a head of an inner post mounted within the axial bore of theproximal sleeve. Further advancement of the stabilizer against the innerpost moves the inner post within the axial bore of the proximal sleeveand moves the distal screw portion mounted to a distal end of the innerpost away from the proximal sleeve.

Advancing the distal screw may include advancing a plurality of outerthreads on the distal screw portion into the bone. Advancing theproximal sleeve includes advancing a plurality of outer threads on theproximal sleeve into the bone. Advancing the stabilizer may includerotating threads of the stabilizer along threads of the axial bore ofthe proximal sleeve.

The method may also include counter-rotating the stabilizer to distractthe proximal sleeve away from the distal screw. Such counter-rotationcauses the stabilizer to pull back on a trap connected to a proximal endof the inner post.

An intervertebral cage of another implementation includes twolongitudinal bar pairs, at least one spacer and at least one separatorfor both lateral and vertical separation. The longitudinal bar pairsinclude an upper bar and a lower bar. The bar pairs are spaced from eachother on opposite sides of a midline vertical plane of the cage. Thespacer is moveable within the space between the longitudinal bar pairsto cause movement of at least a portion of the longitudinal bar pairsaway from each other and from the midline vertical plane. The separatoris moveable between the upper and lower bar pairs of a bar pair to causeseparation between at least a portion of the bars of that longitudinalbar pair.

These and other features and advantages of the implementations of thepresent disclosure will become more readily apparent to those skilled inthe art upon consideration of the following detailed description andaccompanying drawings, which describe both the preferred and alternativeimplementations of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bone screw and drivers;

FIG. 2 is a perspective view of an assembled bone screw from FIG. 1;

FIG. 3 is a perspective view of bilateral insertion of two needles andguide wires into two adjacent vertebrae and through a disc space;

FIG. 4 is a perspective view of a threaded distal tip of a bone screwand a cage and a main shaft sleeved over each of the guide wires of FIG.3;

FIG. 5 is a perspective view of the bone screws of FIG. 4 with athreaded sleeve;

FIG. 6 is a perspective view of the bone screws of FIG. 5 with fastenersattached to their proximal ends;

FIG. 7 is an anti-rotation bone screw;

FIG. 8 is a plan view of a collapsed intervertebral cage configured forinsertion through a small incision;

FIG. 9 is a plan view of the intervertebral cage of FIG. 8 expanded intoa disc space and secured with a pin;

FIG. 10 is a plan view of an intervertebral cage with a door foraccessing a central area of the cage;

FIG. 11 is a side elevation view of an intervertebral cage having awindow;

FIG. 12 is a schematic of a threaded distal tip and a main shaft of abone screw;

FIG. 13 is a schematic of a threaded outer sleeve;

FIG. 14 is a schematic of a fastener;

FIG. 15 is a schematic of drilling a pilot hole into two bones;

FIG. 16 is a schematic of reaming or tapping of the two bones of FIG.15;

FIG. 17 is a schematic of the two bones of FIG. 16 after tapping iscompleted;

FIG. 18 is a schematic of driving of a bone screw into the tapped holeof FIG. 17;

FIG. 19 is a schematic of distracting the two bones of FIG. 18 apart byrotating an outer sleeve of the bone screw;

FIG. 20 is a schematic of attaching a fastener to the bone screw of FIG.19 after distraction;

FIG. 21 is a schematic of compressing the two bones of FIG. 18 togetherby rotating an outer sleeve of the bone screw; and

FIG. 22 is a schematic of attaching a fastener to the bone screw of FIG.21 for further compression;

FIG. 23 is a schematic of two bones attached with a plate and securedwith two anti-rotation screws shown in FIG. 7;

FIG. 24 shows a perspective view of an expanded cage with four links andfour hinges and defining a window subjacent a pin;

FIG. 25 shows a perspective view of a bone screw of anotherimplementation;

FIG. 26 shows an elevation view of the bone screw of FIG. 25;

FIG. 27 shows a partial sectional view of the bone screw of FIG. 25;

FIG. 28 shows an enlarged section view of a proximal end of the bonescrew of FIG. 25;

FIG. 29 shows a perspective view of a trap of the bone screw of FIG. 25;

FIG. 30 shows a plan view of a cap of a connector of the bone screw ofFIG. 25;

FIG. 31 shows a plan view of a proximal sleeve of the bone screw of FIG.25;

FIG. 32 shows an elevation view of the proximal sleeve of FIG. 31;

FIG. 33 shows a perspective view of a stabilizer of a connector of abone screw of FIG. 25;

FIG. 34 is a plan view of the stabilizer of FIG. 33;

FIG. 35 is a perspective view of a distal screw portion of the bonescrew of FIG. 25;

FIG. 36 is an elevation view of the distal screw portion of FIG. 35;

FIG. 37 is an elevation view of an inner post of the bone screw of FIG.25;

FIG. 38 is an elevation view of an assembled connector and inner post ofthe bone screw of FIG. 25;

FIG. 39 is a perspective view of the assembly of FIG. 38;

FIG. 40A is a plan view of a laterally and vertically expandable cage;

FIG. 40B is a perspective view of the expandable cage of FIG. 40A;

FIG. 41A is a plan view the expandable cage of FIG. 40A in a laterallyexpanded configuration;

FIG. 41B is a perspective view of the expandable cage of FIG. 41A;

FIG. 42A is a plan view of the expandable cage of FIG. 41A furthervertically expanded;

FIG. 42B is a side elevation view of the expandable cage of FIG. 42A;

FIG. 43 is a partially disassembled view of the expandable cage of FIG.42A;

FIG. 44 is a further disassembled view of the expandable cage of FIG.43;

FIG. 45 is a plan view of a collapsed, four-bar intervertebral cage;

FIG. 46 is a plan view of the intervertebral cage of FIG. 45 in anexpanded configuration;

FIG. 47 is a perspective view of the intervertebral cage of FIG. 46;

FIG. 48 is a plan view of a collapsed, six-bar intervertebral cage;

FIG. 49 is a plan view of the intervertebral cage of FIG. 48 in anexpanded configuration;

FIG. 50 is a perspective view of the intervertebral cage of FIG. 49;

FIG. 51 is a schematic of another intervertebral cage in a collapsedconfiguration; and

FIG. 52 is a schematic of the intervertebral cage of FIG. 51 in anexpanded configuration.

DETAILED DESCRIPTION OF THE INVENTION

Implementations of the present disclosure now will be described morefully hereinafter. Indeed, these implementations can be embodied in manydifferent forms and should not be construed as limited to theimplementations set forth herein; rather, these implementations areprovided so that this disclosure will satisfy applicable legalrequirements. As used in the specification, and in the appended claims,the singular forms “a”, “an”, “the”, include plural referents unless thecontext clearly dictates otherwise. The term “comprising” and variationsthereof as used herein is used synonymously with the term “including”and variations thereof and are open, non-limiting terms.

A method and system for performing bone fusion and/or securing one ormore bones are disclosed. One or more screws of the system areconfigured to enable compression and distraction to modify the gapbetween the vertebral bodies. An intervertebral cage of the system isconfigured for lateral expansion from a nearly straight configuration toform a large footprint in the disc space.

Generally, for fusion, adjacent vertebrae are stabilized non-invasivelywithout prior destabilization using bilateral screw placement and anexpanding cage, both of which can be combined with the use of bonefilling. Screws are passed from the inferior to superior vertebra, forexample, through a trans-pedicular route so as to avoid neurologicalcompromise. At the same time, the path of screw insertion is oriented toreach superior vertebra.

The cage of the system provides a structural component for forming abony bridge, such as through the use of bone grafting materials, betweenthe vertebrae. The cage is configured for minimally invasive insertion,such as through a small annulotomy and subsequent cage expansion. Thisprovides a large surface area to prevent subsidence and facilitatefusion with reduced disc removal.

The systems and methods also provide the surgeon an ability to performcompression and/or distraction maneuvers during different neurosurgicaland orthopedic procedures with a predictable amount ofcompression/distraction in terms of both distance and force. Althoughdescribed in the context of vertebrae, it should be noted that none ofthe implementations described herein are limited to any particularanatomical bone structure. The bone screws, cages and other componentsdescribed herein may be used on any number of bones or bone fragments,such as a tibia, skull, etc.

As shown in FIGS. 1-2, a bone screw 10 includes a threaded tip 12, amain shaft 14 and a threaded outer sleeve 16. The bone screw 10 may alsoinclude a cage 32 and a fastener 58.

As shown in FIGS. 1-2 and 12, the threaded tip 12 includes a proximalend 28 and a distal end 30. The proximal end 28 is configured forattachment of the main shaft 14, such as by having a threaded axialopening configured to receive a threaded end of the main shaft 14. Thedistal end 30 has a point that is configured for driving into bone, suchas through an existing tapped or drilled hole in the bone, as will beshown below.

The proximal end 28 has a shape and diameter that generally matches anouter shape and diameter of the cylindrical cage 32 and/or a distal end24 of the threaded outer sleeve 16. The proximal end 28 tapers to thepoint at the distal end 30. This can facilitate enlargement of theopening in the bone for subsequent passage of the remainder of the screw10. The outer diameter of the proximal end 28, however, may also belarger than some internal diameter of the cylindrical cage 32, so thatit does not slip distally off of the threaded tip 12.

As shown in FIGS. 1-2 and 12, the main shaft 14 includes a proximal end18 and a distal end 20 and is attached to the threaded tip 12 andextends proximally therefrom. Such attachment can be by threadedinsertion into the threaded tip 12, separate construction and laterpermanent attachment (e.g., welding) or may be integrally formed withthe threaded tip 12. The main shaft 14 has a diameter that is configuredto fit through axial openings extending through the remaining componentsof the screw 10.

The main shaft 14 at its proximal end 18 has a threaded portion with arelatively high number of threads per inch. The proximal end 18 alsodefines a driver interface, such as a non-circular shaped receptacle ora non-cylindrical outer shape (e.g. square or hexagonal) that isconfigured to accept or slide into a driver for rotational advancementof the main shaft 14 with the threaded tip 12 at its distal end.

The main shaft 14 may also include a stop member 26 coupled thereto. Thestop member 26, for example, may be an annular ring positioned abouthalf way between the proximal end 18 and the distal end 20, as shown inFIG. 1. The stop member 26 may be separately attached or integrallyformed with the main shaft 14. Other shapes are possible for the stopmember 16, including shapes that match an outer shape and max diameterof the threaded outer sleeve 16 at its distal end 24 or a proximal end34 of the cylindrical cage 32 so as to facilitate its passage through abone opening. Generally, the stop member 26 is configured to act as astop for distal travel of the threaded outer sleeve 16 over the mainshaft 14 and therefore should have a larger diameter and/or incompatibleshape with respect to an axial opening 26 of the threaded outer sleeve16.

As shown in FIG. 1, the cage 32 includes the proximal end 34 and adistal end 36. The cage 32 has a shape (e.g., cylindrical) and outerdiameter that is configured to trail the proximal end 28 of threaded tip12 smoothly upon insertion. The cage 32 has defined axially, between theends 34, 36, an opening that is configured to allow its passage over themain shaft 14 and possibly the stop member 26 to abut (by being somewhatsmaller than a maximum diameter of) the proximal end 28 of the threadedtip 12. Other cage shapes are also possible, such as a square ornon-cylindrical cross-section, wherein the shapes are configured toreceive bone graft material or bone growth promoting materials such asbone morphogenic protein (BMP).

The cage defines lateral or side holes or openings 38 which allow bonegrowth promoters held within the cage to leak, diffuse or otherwiseaccess (or be accessed by) adjacent bone structures so as to promotefusion. The lateral openings may be, for example, square openings whenthe cage 32 is formed of axially aligned rings connected by radiallyspaced longitudinals. The lateral openings 38 may also be other shapesand distributions, such as cylindrical openings or irregularly shapedand placed openings.

The distal end 36 of the cage 32 may include one or more lockingsurfaces configured to mate with a corresponding locking surface on theproximal end 28 of the threaded tip 12.

As shown in FIGS. 1-12 and 13, the threaded outer sleeve 16 has aproximal end 22 and the distal end 24. The axial opening 26 is definedaxially through the threaded outer sleeve 16 and extends between theproximal and distal ends 22, 24 of the outer sleeve. The axial opening26 has a diameter sufficient to receive and allow passage of theproximal end 18 of the main shaft 14. And, the threaded outer sleeve 16is configured to extend over and allow the threaded outer sleeve 16 tofreely rotate about the proximal end 18 of the main shaft 14.

The threaded outer sleeve 16 may have threads that match the threads ofthe threaded tip 12 and a maximum and minimum diameter that are the sameas the diameters of the proximal end 28 of the threaded tip 12. Thethreaded outer sleeve 16 may also have a larger diameter (maximum orminimum) than the diameter of the threaded tip 12 to facilitaterotational locking and/or secure fixation of the threaded outer sleeve16.

As shown in FIGS. 1-2 and 14, the fastener 58 is a nut having a threadedinner opening and outer driving surfaces. The fastener 58 is configuredfor attachment to the proximal end of the main shaft 14 and engagementof the threads thereon to lock the threaded outer sleeve 16 against thestop member 26.

As shown in FIG. 4, the threaded tip 12 and the main shaft 14 may definea central wire opening for passage over a guide or working wire 40.

As shown in FIGS. 18 and 19, the system may also include an outer driver42 and an inner driver 44. The inner driver 44 has a driving shaft 46and a driving tip 48 that is configured to mate with the drivingsurfaces or opening on the proximal end 18 of the main shaft. At itsproximal end (not shown) the inner driver 44 (and the outer driver 42)may have a grip or handle configured for hand driving and/or beconfigured to mate to a motorized driver.

The outer driver 42 includes a tubular shaft 50 and a driving tip 52.The tubular shaft 50 of the outer driver 42 is configured to sleeve overthe proximal end 22 of the main shaft. The driving tip 52 is configuredto mate with the driving surfaces of the proximal end 22 of the threadedouter sleeve 16 and/or with the driving surfaces of the fastener 58. Inthis manner, the outer driver 42 is configured to advance the fullyassembled bone screw 10.

FIGS. 15-22 show use of the bone screw 10 to connect and/or compress ordistract an inferior vertebra 54 and a superior vertebra 56. As shown inFIG. 15, a pilot hole is formed by use of a small drill bit whichadvances first through the inferior vertebra 54 and into the superiorvertebra 56. As shown in FIGS. 16 and 17, the pilot hole is reamed witha remaining drill bit that is oversized relative to the small drill bit.The reamed hole approximates the diameter and thread pitch of the bonescrew 10 components for easier insertion.

As shown in FIG. 18, the assembled screw 10, including threaded outersleeve 16 sleeved over the main shaft 14 up to and abutting the stopmember 26 and locked against the stop member 26 by the attached fastenernut 58, is advanced through the inferior vertebra 54 and the superiorvertebra 56 using the inner driver 44. Notably, once the screw 10 isassembled and locked, the cylindrical threaded outer sleeve 16 is lockedbetween the nut 58 and the stop member 26 on the main shaft 14 and isfunctioning as a regular screw.

As shown in FIG. 19, the fastener nut 58 has been removed (allowing thecylindrical threaded outer sleeve 16 to turn around the main shaft) andthe outer driver 42 is engaged to the proximal end 22 of the threadedouter sleeve 16. While the inner driver 44 holds the main shaft 14still, the outer driver 42 is rotated clockwise against the stop member26 to distract the inferior vertebra 54 away from the superior vertebra56.

As shown in FIG. 20, once the desired distraction distance isaccomplished, the fastener nut 58 is reattached to the proximal end 18of the main shaft 14. This stops relative rotation of the sleeve 16 andthe main shaft 14 and hence motion between the vertebrae 54, 56.

As shown in FIG. 21, the vertebrae 54, 56 (or other bones as the casemay be) can be compressed relative to each other. The inner driver 44holds the main shaft 14 still and the outer driver 42 is rotatedcounter-clockwise away from the stop member 25. Then, as shown in FIG.22, the fastener nut 58 is attached to the proximal end 18 of the mainshaft and as it is advanced thereon, the cylindrical outer sleeve 16 isadvanced toward the stop member 26 and the vertebrae 54, 56 arecompressed toward each other.

As shown in FIG. 3, several screws 10 may be deployed to bridge twovertebrae 54, 46 across the disc space at an angle using a posteriorapproach or a bilateral, transpedicular approach. As shown in FIG. 3,the driving direction is an inferior to superior trajectory startingwith two small 1 cm incisions in the lumbar regions. A JAMSHIDI needleis inserted through each of the incisions at the desired angle, thestylet removed and a K-wire inserted through the central opening of theneedle. The needle is then removed.

As shown in FIG. 4, the threaded tip 12, the main shaft 14 and thecylindrical cage 32 are advanced, using the inner driver 44, over theK-wire through the inferior vertebra 54, the disc space and into thesuperior vertebra 56. The cylindrical cage 32 may have been packed witha bone graft and/or fusion material that can communicate through holesin the cage. As shown in FIG. 5, the outer driver 42 is engaged on thethreaded outer sleeve 16 and over the main shaft 14 to drive thethreaded outer sleeve through the hole in the inferior vertebra 54.

As shown in FIG. 6, the locking nut 58 is attached to the main shaft 14and the K-wire is withdrawn.

As shown in FIG. 7, the screw 10 may also include an oppositely threadedouter sleeve 16. The main shaft 14 includes no stop member 26 and has atits end attached the locking nut 58 to form a solid screw. Attachment ofthe threaded outer sleeve 16 is facilitated by its initial ability tofreely rotate about the main shaft 14 once the threaded tip 12 and mainshaft 14 are inserted into a bone. Then, reverse-threaded outer sleeve16 can be counter rotated until it advances to the proximal end of thethreaded tip 12. The locking nut 58 is then attached.

Because of the reverse threading of the threaded tip 12 and the outersleeve 16, the screw 10 resists rotation when in a single structure,such as a single bone. Thus, as shown in FIG. 23, a plate 60 can beattached to bridge two bones with just two anti-rotation screws 10, onein each bone, eliminating rotational instability. Normally, twoconventional screws are required in each bone to stop rotation of theplate relative to the bone. The anti-rotation screw 10 and the plate 60may have structure for engaging each other, such as a correspondingnon-cylindrical shape, to counter rotation of the plate and screwrelative to each other.

As shown in FIG. 9, the system may use or include an intervertebral cage62 that includes a plurality of links 64 and hinges 66, such as fourlinks connected by hinges to form a four-bar linkage. Each of the linkshas a height configured to hold endplates of two adjacent vertebrae 54,56 apart from each other a desired distance. Two of the links may have afirst length and another two of the links may have a second length, notequal to the first length, so as to form a rectangular shape orequilateral shape.

Advantageously, the relatively thin dimensions of the links 64 and theflexibility of the hinges 66, allow the cage to be folded relativelyflat upon itself, as shown in FIG. 8. This configuration allows the cage62 to be inserted through a small incision into the disc space orbetween two adjacent bones. When deployed, the first length (and the twocorresponding opposing links 64) extends anterior-posteriorly within thedisc space between the end plates of the vertebra 54, 56. The secondlength extends medio-laterally within the disc space thereby providing arelative large footprint.

As shown in FIG. 9, the cage 62 may include a pin 68 that is configuredto engage an opening in two adjacent ones of the links 64, across one ofthe hinges 66, so as to lock the adjacent links into a predeterminedangular position, such as 90 degrees. Defined in the pin 68 may be adetent that is engaged by one or both of the links 64 so that the pin 68locks into position within the opening, wherein it can resist backingout from the opening. The pin 68 may also include a spring-biased rivet,ball or other engagement member configured to lock the relative slidingmotion of the pin 68 once it has reached a predetermined position. Thespring biased locking member may also be resident on one of the linksand extend into the pin detent.

When deployed, the cage 62 has an open middle and may include a window72 in one of the links 64 for providing access to the open middle, asshown in FIG. 11. Also, a door 72 may be included, wherein the door isconfigured to open on its own hinge and provide access to the openmiddle, as shown in FIG. 10. The door 70, or the window 72, may be usedto access the open middle and place a “bone filling” such as a bonegraft and/or growth promoting materials therein.

A method of using the cage 62 includes collapsing the links 64 into thelinear arrangement, as shown in FIG. 8, and inserting the lineararrangement through a small incision into the disc space. Then, the twoproximal links 64 of the cage 62 are pried apart (such as by using longinstruments) to form a proximal angle, such as a 90 degree angle.

Simultaneously, in the case of a four bar linkage, the opposite distallinks 64 open at the opposite hinge to form a distal angle because thedistal links 64 are urged open with ends of the proximal links throughthe middle hinges. Also in the case of a four bar linkage, the distalangle is equal to the proximal angle.

Once the cage 62 is expanded in the disc space, the pin 68 is insertedthrough the surgical opening through the opening in the proximal twolinks 64 until its detent or spring-loaded mechanism locks into place,as shown in FIG. 9.

To facilitate fusion, the window 72 is accessed for insertion of a bonefilling into the center opening of the cage 62, as shown in FIGS. 10 and11. If the door 70 is present, it is opened, the bone filling is added,and the door is closed over the window 72.

The window 72 may also be positioned, as shown in FIG. 24, subjacent theopening for the pin 68. The pin may include threads and extend throughan opening above the window allowing for a more compact access for boththe pin and the bone filling procedure. Further, tops and bottoms of thelinks 64 may have defined on them serrations or ridges to improvefixation.

Further advantageously, placement of the cage 62 may be combined withattachment of bilateral bone screws 10 (either before or after cage 62placement) as described above for improved stability and fusionpotential even through minimal incisions and relatively little discremoval.

An additional implementation of a bone screw 110 is shown in FIG. 25.The bone screw 110 includes an inferior or proximal portion 112, asuperior or distal portion 114 and a connector 116. The use of proximaland distal herein is relative to the healthcare worker or surgeon usingthe device. Inferior and superior are relative to the patient and assumethe screw is being inserted through the vertebral bodies in a superiordirection—towards the patient's head. Of course, these directions arefor reference

As shown in FIGS. 27, 31 and 32, the proximal portion 112 has a sleeveshape (generally) and includes a proximal end 118 and a distal end 120.The proximal end 118 includes a hexagonal outer diameter defining atransverse U-shaped slot 122 that extends through opposite walls of thehexagonal outer diameter. The hexagonal outer shape is configured to fitan 8 mm socket driver for advancement of the proximal portion 112. Thehexagonal outer diameter may have a diameter of 7.75 mm to 7.95 mm forexample for mating with an 8 mm driver.

The U-shaped slot has a width of about 3.95 to 4.20 mm. Defined withinthe proximal end 118 is a cylindrical bore 124 having a plurality ofthreads extending around the inside diameter. The threads within thecylindrical bore 124 may have a pitch of about 1 mm, a major diameter of6.80 to 7.00 mm and a minor diameter of 6.30 to 6.50 mm. The cylindricalbore 124 has a step change in diameter where the threads end near thebottom of the bore and a second step change to a smaller 5.31 mm.(Tolerances for the measurements herein are +/−0.10 mm for a two placedecimal and +/−0.05 for a three place decimal.)

The distal end 120 of the proximal portion 112 includes a graduallytapering cylindrical shaft. For example, the taper may be 0.5 degrees.The distal end 120 may have a length of 25 mm and a plurality of threadsextending around its outside surface. The threads may, for example, havea pitch of 2.5 mm, a major diameter of 7.35 mm and a minor diameter of6.75 mm. As shown in FIG. 27, the distal end 120 includes a cylindricalbore 126 that extends the length of the distal end 120 of the proximalportion 112.

As shown in FIGS. 27, 35 and 36, the superior or distal portion 114includes a screw portion 106 and an inner or main shaft or post 108.

As shown in FIGS. 27 and 37-39, the inner post 108 of the distal portion114 includes a distal end 128 and a proximal end 130. The distal end 128of the inner post 108 includes a small diameter cylindrical section(e.g., 4.90 mm) with a chamfered free edge. For example, the chamfer maybe 45 degrees. Defined within the distal end 128 of the inner post 108is a 1.50 mm cylindrical bore. The distal end 128 of the inner post 108may be 9.50 mm long and may include a bore 132.

The proximal end 130 of the inner post 108 has a shaft portion 134 thathas a cylindrical shape and extends along the middle of the inner post108. The proximal end 130 also includes a driving end 136 on its mostproximal, free end, as shown in FIG. 29. The driving end 136 has a head138 which flares out to a diameter of 6.19+/0.10 mm for example. Thelength of the head 138 may be 3 mm for example. The transition betweenthe shaft portion 134 and the head 138 is defined by a convex taper,such as a taper with a 1.50 mm radius.

The driving end 136 may also include a driver receptacle 140, such asthe one shown in FIG. 28, with a hexagonal shape configured to receive adriver, such as an Allen wrench or screw driver with a hexagonal drivingend. Notably, other non-cylindrical shapes could be defined by thedriver receptacle 140 to transmit torque from a driver.

The screw portion 106 includes a proximal end 142 and a distal end 144.The proximal end is configured to facilitate bone ingrowth or otherfixation of the bone screw 110 once implanted. For example, the proximalend 142, as shown in FIG. 30, may have a cylindrical shape with 20 mmlength. The proximal end 142 may be a cage (as described above) forholding bone growth promoting compounds. Or, the proximal end 142 mayhave a knurled or textured outer surface that is configured to promotebone adhesion. The knurl for example may have a diamond shaped latticethat is configured to hold bone chips in the grooves of the knurl.

Defined within the proximal end 142 of the screw portion 106 may be aslightly tapering bore 150 having a proximal diameter of about 4.80 mmand tapering at 0.5 degrees along about a 10.00 to 10.40 mm length. Thistaper is configured for a press-fit reception of the inner post 108which has a 4.90 mm diameter.

The distal end 144 of the screw portion has a conical shape that tapersgently at mid-shaft 146 and tapers aggressively near a point 148. Forexample, the mid-shaft 146 may taper at 1 degree along about 12.5 mm andthen at 25 degrees to the distal-most point. Threads extend along thedistal end 144, starting at its base and may have a pitch, for example,of 2.50 mm, a major diameter of 6.10 mm and a minor diameter of 5.40 mm.

As shown in FIGS. 27-30, 33, 34 and 38-39, the connector 116 includes atrap 152 and a locking nut or stabilizer 154. Generally, the trap 152 isconfigured to couple to the remainder of the bone screw 110 and tocontain the stabilizer 154. The trap, as shown in FIG. 29, includes abase 156, a pair of arms 158 and a cap 160. The base 156, for example,may have a circular ring shape defining a central bore or opening. Thering shape, for example, may have a radius of about 3.20 mm and the borea diameter of 5.31 mm. The thickness or height of the base 158 may beabout 1.50 mm. The bore may also include a 45 degree chamfer.

The arms 158 extend upwards (proximally) from the base 156 and areattached on opposite sides of the base 156. The arms 158 have two angledflats defining their outer surfaces and partial cylindrical arcsdefining their inner surfaces, the cylindrical arcs tracing a radius of3.50 mm of a circle. At their proximal-most free edge is defined a lip162 which is a step down to a slightly bigger radius (3.60 mm) partialcylindrical surface. The arms have a length of about 11 mm, or 9.50 mmmore than the height of the base 156. The arms also have a width ofabout 3.85 mm or 3.95 mm.

Defined near the proximal or top ends of the arms 158 are a pair ofaligned, concentric pin holes 164. The pin holes 164 have a radius ofabout 0.75 mm. The pin holes 164 are centered at the apex between thetwo outer angled flat surfaces of the arms 158.

As shown in FIGS. 28 and 30, the cap 160 may include a cylindrical ring168 with a pair of enlarged ears 166. The radius of the ring 168 of thecap 160 may, for example, be about 3.15 mm. The ears 166 are portions ofan outer, larger cylinder and extend from opposite sides of the ring168. Defined through the ears 166 are a pair of pin holes 164 that areaxially aligned with each other on opposite sides of the axis of the cap160. The radius of the ears 166 is configured to match the radius of theinner opening of the arms 158 proximal the lip 162. For example, theears may have a 3.60 mm radius. The matched radius allows the cap to beseated on the lip 162

As shown in FIGS. 33-34, the stabilizer 154 has a cylindrical shape witha plurality of threads extending around its out surface. The threads,for example, have a pitch of 1 mm, a major diameter of 6.60 mm to 6.79mm and a minor diameter of 6.10 mm to 6.29 mm. The length or height ofthe cylinder is about 3 mm. Defined in the center of the stabilizer is adriver receptacle 170, such as a 5/32 hexagonal receptacle for an Allenwrench. Driving of the stabilizer, as will be described in more detailbelow, drives compression and distraction of the proximal portion 112and distal portion 114 of the bone screw 110.

As shown in FIGS. 38-39, the trap 152 and stabilizer 154 may be firstassembled to the head 138 of the inner post 108. For example, the distalend 128 of the inner post 108 may be slipped through the opening in thebase 156 of the trap until the head 138 is positioned between the arms158. (The head 138 is too large to pass through the base 156 ring.) Thestabilizer 154 may then be advanced, such as by an Allen wrench, alongthe threads within the arms 158 until it abuts the head 138. Then, thecap 160 may be slipped in between the upright arms 158 of the trap 152until the ears 166 hit the lip 162. The pin holes 164 of the cap 160 andarms 158 are aligned. Optionally, a pin may be advanced through the pinholes 164. The pin allows for deformation in the inner post during thepressure fitting. This connection between the inner post and thesuperior screw may also be connected together by a rivet or otherfasteners.

As shown in FIG. 27, the inner post 108 and connector 116 may then beassembled by insertion through the proximal portion 110 of the bonescrew 110. In particular, the distal end 128 of the inner post 108 maybe inserted through the cylindrical bores 124, 126 of the proximalportion 112 of the bone screw 110. As the inner post 108 is advanced,the arms 158 of the trap 152 are aligned with and inserted into theU-shaped slots 122 of the proximal end 118. Further advancement mayinclude rotating or driving the stabilizer 154 so that its threadsadvance along the inner threads on the inside of the proximal end 118.

The distal end 128 of the inner post 108 is then press fit into the bore150 of the proximal end 142 of the screw portion 106. Rather than apress fit, other attachments could be employed such as threadedfittings, clamps, adhesives, etc. Once this assembly is finished, thebone screw 110 is ready for use in attaching, contracting or distractingvertebrae as described, for example, in the procedures disclosed for thebone screw 10 above.

The entire bone screw 110 may be driven by way of the hexagonal shape ofthe proximal end 118 of the proximal portion 112 of the bone screw.

After driving into two bone pieces, such as two adjacent vertebra orbone fragments, the relative positioning of the proximal portion 112 anddistal portion 114 of the bone screw 110 (and hence of the adjacent bonefragments) may be controlled by insertion of a driver through theopening in the cap 160, the driver receptacle 170 of the stabilizer 154and into the driver receptacle 140 of the inner post 108. Rotating thedriver causes the threads on the stabilizer 154 to advance (or retractif counter-rotating) along the threads of the proximal portion 112. Thiscauses the proximal portion 112 to slide along the inner post 108 of thedistal portion 114.

Counter rotation of the stabilizer 154 distracts the proximal and distalportions because the stabilizer backs into the cap 160 of the trap 152.This pulls on the arms 158 and base 156 of the trap which is nestedaround the head 138 of the inner post 108. As the connector assemblymoves out of the proximal portion 112, the screw portion 106 on theopposite end of the inner post 108 is pulled closer to the proximalportion.

FIGS. 40A and 40B illustrate an example expandable intervertebral cagein an unexpanded state. FIG. 40A is top view illustration of the exampleexpandable intervertebral cage 200. The cage is designed forimplantation between two vertebrae of a patient at any location alongthe spine. For example, the cage can be implanted between two adjacentcervical, thoracic, lumbar, or sacral vertebrae. The cage is optionallyused to fuse two adjacent vertebrae. The cage is optionally used toadjust the spacing between two adjacent vertebrae. The cage isoptionally used with additional pharmacological, biological ormechanical agents administered at the site or in proximity to the siteof implantation.

The cage 200 is optionally expandable both horizontally and verticallyas will be described below. Optionally the cage is inserted between twoadjacent vertebrae of the patient in a non-expanded state. An example ofa horizontally expanded, but vertically non-expanded, state is shown inFIGS. 41A and 41B.

Once positioned as desired by a medical professional, the cage 200 canbe expanded in a horizontal direction; for example, in the horizontalplane of the intervertebral space in which the cage is located. The cage200 can also be optionally expanded in a vertical direction, which canincrease the vertical separation between the adjacent vertebrae.Optionally, the horizontal expansion is performed before the verticalexpansion. Optionally a single actuator is used to first causehorizontal expansion followed by vertical expansion. In this way, a lowheight and width profile of the unexpanded cage can be used forimplantation and then with use of the single actuator, the height andwidth profile can be expanded as desired.

The cage 200 includes two pairs of longitudinal bars. Each pair includesan upper bar 202 and a lower bar 203 (as shown, for example, in FIG.41B). The pairs are spaced from one another across the vertical midlineplane A-A of the cage. The spacing across the vertical midline planecreates a space 207 that can be widened when the cage is expanded in thehorizontal direction.

To cause movement of each bar pair away from the vertical midline plane,the cage includes at least one spacer 204. The one or more spacer 204 ismoveable into and between the space 207 between the bar pairs. The sizeof the spacer 204 prior to horizontal expansion is larger than width ofthe space 207. To cause expansion, one or both of the spacers 204 aremoved into the space 207, which urges the bars horizontally away fromthe midline plane A-A. Optionally, a surface of a spacer 204 is curvedand corresponding surfaces of the bars are also curved. When the curvedsurfaces contact each other it facilitates entry of the spacer 204 intothe space 207 and horizontal separation of the bar pairs.

As mentioned above, the cage 200 can also be expanded vertically. Forexample, the cage 200 optionally includes one or more separators 206. Inthe example cage 200 shown in FIGS. 40A-44, there are four separators.

Each separator 206 is positioned such that it can be moved between thebars (202 and 203) of the cage. In this regard, a first separator ispositioned at a first end of one of the bar pairs for movement betweenthat pair of bars, a second separator is positioned at a first end ofthe opposite bar pair for movement between that pair of bars, a thirdseparator is positioned at a second end of one of the bar pairs formovement between that pair of bars, and a fourth separator is positionedat a second end of the opposite bar pair for movement between that pairof bars.

Each separator can be advanced between the individual bars at theirgiven location. The separators have a height profile that is larger thanany spacing between the upper 202 and lower bars 203 when the cage hasnot been vertically expanded. When one or more separator is advancedbetween the upper and lower bars, therefore, the bars are urged toseparate, resulting in vertical expansion of the at least that bar pair.

Each separator 206 optionally has the same vertical or height profile sothat when all four separators are advanced between the bars, the barpairs symmetrically expand vertically. Optionally, however, one or moreseparator can have a different vertical or height profile from one ormore of the other separators. The differing vertical or height profilesoptionally result in an asymmetric vertical expansion of the cage whenthe separators are advanced between the bars. For example, a separatorwith a larger vertical dimension results in greater verticaldisplacement between the bars at the location where it is advancedbetween the bars, while a separator with a smaller vertical dimensionresults in a smaller vertical displacement between the bars at thelocation where it is advanced between the bars. Therefore, by selectingdifferent sizes of separators in combination different asymmetricvertical expansion profiles are achieved. Similarly, the width profileof the spacers 204 may also differ. In this way, asymmetric horizontalexpansion is optionally accomplished.

Each spacer 204 is optionally connected via two connectors 208 that areon the same end of the bars. A spacer 204 is connected via two pivotpins 210 to the connector, for example, allowing the spacer to pivotrelative to each connector. The connectors are also pivotably connectedto the separators 206 located on the same end of the bars.

A threaded rod 220 (shown, for example, in FIGS. 41A, 43 and 44)optionally connects with the two spacers 204. By actuating the threadedrod 220, for example by rotating it at point 222, the two spacers aremoved towards each other between the bar pairs resulting in separationof the bar pairs away from the vertical midline plane. The spacers 204,for example, may be drawn to each other by having different directionthreads within their respective openings.

As the spacers advance towards each other, the connectors pivot relativeto the spacers 204 and to the separators 206. As shown in FIG. 40A, themidline of each connector is acutely angled relative to the verticalmidline plane of the cage. As shown in FIG. 41A, as the spacers areadvanced closer to one another and the bar pairs separate horizontally,eventually the connectors rotate to a more closely perpendicularorientation relative to the vertical midline axis.

During this movement of the spacers, from the position shown in FIG. 40Ato the position shown in FIG. 41A, the separators remain substantiallyin the same position, due to the free pivoting of the connectors aboutthe pivot points (210 and 212). Because there has been movement of thespacers towards each other but the separators have stayed substantiallystationary, the cage undergoes horizontal expansion without substantialvertical expansion. A side view of the orientation of FIG. 41A, wherehorizontal expansion has occurred but vertical expansion has notoccurred is shown in FIG. 41B.

As the spacers 204 are further advanced towards each other, theconnector continues to pivot relative to the spacer and the separatorsand horizontal expansion progresses without substantial verticalexpansion. Eventually the connectors cannot rotate any further as theycontact one or more stop surfaces of the cage. For example, the stopsurface is optionally a portion of the spacer and/or a surface of a barthat limits the ultimate extent of rotation. Once rotation has beenstopped, continued actuation of the threaded rod 220 results inadvancement of the separators 206 between the rods rather than furtheradvancement of the spacers 204 towards each other. The result is that asthe threaded rod is further actuated, the cage stops its horizontalexpansion and begins a substantial vertical expansion as the separators206 move between the rods to urge them apart vertically. In this way,the cage 200 is optionally expandable both horizontally and vertically.The horizontal expansion can occur prior to any substantial verticalexpansion of the cage. FIG. 42B shows a side view after horizontal andvertical expansion.

As shown in FIG. 43, the separators 206 optionally have a sloped frontsurface with a lower vertical rise towards the front of each spacer anda higher vertical rise towards the back of each spacer. Optionally, asalso shown in FIG. 43, the slope is stepped with each step beingsequentially higher. In this regard, as a separator is advanced betweenthe bars, vertical separation between the bars at that location of theseparator increases until the portion of the separator having itsmaximal height dimension is positioned between the bars, or until adesired vertical separation between the bars is achieved. In addition,when the slope is stepped, the vertical separation between the bars at alocation of the separator can be adjusted to progressively greateramounts by progressively advancing new steps between the bars.

Each bar, for example, as shown in FIGS. 43 and 44, optionally includesgrooves 226 to accept the advancing separators 206. The groovesoptionally include a complementary shape to the separator that is beingadvanced there into the groove.

Another implementation of the intervertebral cage 62 is shown in FIGS.45-50 that include the use of a diagonally oriented draw bolt 80. FIGS.45-47, for example, show a four-bar linkage (similar to the cagedescribed above) that includes four links 64 interconnected by hinges66. Two corners of the cage 62, however, are transfixed by the draw bolt80 which includes a shaft 82 and a pair of nuts 84.

The shaft 82, for example, may be a threaded rod that is configured toextend through threaded openings in the nuts 84. The nuts 84 arepositioned at the two diagonally opposing corners of the four-barlinkage. Each nut includes a pin 68 that extends into adjacent linkageends that sandwich the nut between them. In this manner, the twoadjacent links 64 can rotate relative to the nut 84. Each of the linksalso may include a scallop 86 or other adaptive space configured toallow the draw bar to achieve a collapsed position, such as is shown inFIGS. 45 and 46. The hinges 66 not transfixed are comprised of a pin 68extending through a collinear opening in interdigitated portions of theadjacent ends of the links, as shown in FIG. 47.

A portion of the shaft 82 of the draw bolt 80 may have an extendedlength off of one hinge. This facilitates rotation of the shaft 82 afterimplantation of the cage 62 in the collapsed condition, such as is shownin FIG. 45. The two nuts 84 are drawn toward each other by rotation ofthe shaft 82 which may have different handed threads (or the nuts havedifferent handed threads) to cause them to move toward each other withuni-directional rotation. Rotation of the shaft 82, therefore, mayresult in the expanded configuration shown in FIGS. 46 and 47.

Additional numbers of links 64 could be employed, such as 5, 6, 8 oradditional links, although even link numbers have symmetrical expansioncharacteristics. FIGS. 48-50, for example, show use of six links 64moving from a collapsed configuration (FIG. 48) to an expandedconfiguration (FIGS. 49-50) by way of rotation of the shaft 82 of thedraw bolt 80.

FIGS. 51 and 52 show a variation wherein the draw bolt 80 includes athreaded shaft 82 which can reciprocate into and out of an internallythreaded sleeve 88.

A number of aspects of the systems, devices and methods have beendescribed. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe disclosure. Accordingly, other aspects are within the scope of thefollowing claims.

That which is claimed:
 1. A cage for placement between two vertebralendplates, the cage comprising: at least four links, and a plurality ofhinges, one of the hinges interconnecting each adjacent pair of links;wherein the links have a height configured to hold the vertebralendplates apart a therapeutic distance.
 2. The cage of claim 1, whereintwo of the links have a first length and another two of the links have asecond length and the first length is not the same as the second length.3. The cage of claim 2, further comprising a pin and wherein twoadjacent links define an opening configured to receive the pin, whereinthe pin is configured to lock the adjacent links into a predeterminedangular position.
 4. The cage of claim 3, wherein one of the pin or theopenings includes a locking mechanism configured to secure the pinwithin the openings.
 5. The cage of claim 4, wherein the lockingmechanism is a detent in the pin.
 6. The cage of claim 4, wherein thelocking mechanism is a spring-biased engagement member.
 7. The cage ofclaim 3, wherein the predetermined angular position is 90 degrees. 8.The cage of claim 7, wherein the first length is configured to extendwithin an anterior-posterior distance of the endplates and the secondlength is configured to extend within a medial-lateral distance of theendplates.
 9. The cage of claim 1, wherein one of the links defines anopening therein configured to receive a bone filling.
 10. The cage ofclaim 9, further comprising a door configured to occlude the opening.11. The cage of claim 10, further comprising a door hinge connected tothe door.
 12. The cage of claim 1, wherein the links are configured tocollapse into a relatively linear configuration with pairs of the linkspositioned an adjacent each other.
 13. The cage of claim 1, furthercomprising a draw bolt configured to draw two hinges toward each other.14. The cage of claim 13, wherein the draw bolt includes a threaded drawshaft extending through two nuts, wherein each nut is positioned at arespective one of the two hinges.
 15. The cage of claim 14, wherein eachof the nuts is sandwiched between free ends of two adjacent links. 16.The cage of claim 15, wherein the links define one or more scallopsconfigured to facilitate a more linear collapse of the links.
 17. Thecage of claim 16, wherein rotation of the draw shaft in one direction isconfigured to move the nuts toward each other.
 18. The cage of claim 13,wherein the at least four links are six links.
 19. The cage of claim 15,wherein the bolts are positioned at opposing hinges.
 20. The cage ofclaim 13, wherein the draw bolt includes a threaded draw shaft and aninternally threaded sleeve.
 21. The cage of claim 20, wherein the drawshaft and sleeve meet at an approximately central location within aspace defined by the links.
 22. The cage of claim 13, wherein rotatingthe draw bolt in one direction forms a rectangular configuration. 23.The cage of claim 22, wherein rotating the draw bolt in an oppositedirection collapses the links into a more linear configuration.